Đáp án+Giải thích các bước giải:
`A=sin^2 11^@+sin^2 21^@+sin^2 31^@+sin^2 45^@+sin^2 59^@+sin 69^@+sin^2 79^@`
`A=sin^2 11^@+sin^2 21^@+sin^2 31^@+(sqrt2/2)^2+cos^2 11^@+cos^2 21^@+cos^2 31^@`
`A=1+1+1+1/2`
`A=7/2`
`B=sin^2 15^@+sin^2 75^@-(2coss49^@)/(sin41^@)+tan26^@.tan64^@`
`B=sin^2 15^@+cos 75^@-(2sin41^@)/sin41^@+tan26^@.cot26^@`
`B=1-2+1=0`
`C=(3cot77^@)/(2tan13^@)-(cos^2 26^@+cos^2 64^@-cos^2 71^@-cos^2 19^@)/(sin^2 34^@+sin^2 56^@+sin^2 15^@+sin^2 75^@)`
`C=(3tan13^@)/(tan13^@)-(cos^2 26^@+sin^2 26^@-sin^2 19^@-cos^2 19^@)/(sin^2 34^@+sin^2 56^@+sin^2 15^@+sin^2 75^@)`
`C=3-(1-1)/(sin^2 34^@+sin^2 56^@+sin^2 15^@+sin^2 75^@)`
`C=3-0=3`
